Evocalcet with vitamin D receptor activator treatment for secondary hyperparathyroidism

This ad hoc analysis of a previously conducted phase 3 head-to-head comparison study of evocalcet and cinacalcet in secondary hyperparathyroidism patients undergoing maintenance hemodialysis evaluated the efficacy and safety of combined once-daily oral evocalcet and intravenous vitamin D receptor activator treatment stratified by weekly vitamin D receptor activator dose (117, 45, and 91 patients in no, low [< 1.5 μg], and high [≥ 1.5 μg] dose groups, respectively). Effects of vitamin D receptor activator were assessed on the basis of intact parathyroid hormone, corrected calcium, phosphorus, and fibroblast growth factor-23 levels; percent changes from baseline; proportions of patients who achieved target intact parathyroid hormone, corrected calcium, and phosphorus at Weeks 28–30; and adverse drug reactions. Intact parathyroid hormone, corrected calcium, phosphorus, and fibroblast growth factor-23 levels decreased in all groups; phosphorus and fibroblast growth factor-23 levels remained high in the high dose group. In the low and high dose groups, greater proportions of patients achieved the corrected calcium target compared with the no dose group (p = 0.043). Ratios of intact-to-C-terminal fibroblast growth factor-23 decreased in all groups. In low and high dose groups, hypocalcemia was less common than in the no dose group (p = 0.014). Evocalcet with concomitant vitamin D receptor activator demonstrated benefits such that more patients achieved the corrected calcium target and exhibited decreased fibroblast growth factor-23 synthesis; the incidence of hypocalcemia also decreased. Clinical trial registration: ClinicalTrials.gov (NCT02549391) and JAPIC (JapicCTI-153013).


Introduction
Patients with severe chronic kidney disease requiring dialysis exhibit a decline in renal function that controls calcium and phosphate metabolism. This impairment subsequently causes Study procedure. Detailed study procedures of the phase 3 head-to-head comparison study were described previously [26]. Briefly, the randomized, double-blind, intrapatient doseadjustment, parallel-group study comprised a 28-week dose adjustment period (Week 0 to 1 day before Week 28) and a 2-week evaluation period (Week 28 to Week 30). During the dose adjustment period, the starting dose of once-daily oral evocalcet was determined based on the serum intact PTH level 1 week prior to treatment initiation: patients with < 500 pg/mL received 1 mg/day and those with � 500 pg/mL received 2 mg/day that was further adjusted at 1 mg increments up to 8 mg on the day of dialysis based on the dose adjustment criteria.
Concomitant medication and therapy, including cinacalcet (from 2 weeks prior to screening to the end of the study), bisphosphonates, denosumab, teriparatide, and parathyroid intervention (from 24 weeks prior to screening to the end of study), and peritoneal dialysis (between Week 12 and Week 30), were prohibited. Changes in prescribed dialysis conditions (dialysate calcium concentration, dialyzer, dialysis time, and number of dialysis sessions per week) were prohibited from 2 weeks prior to screening to the end of the study.
During the period from 2 weeks before screening until the end of the study, initiation of or changes in preparation, dose, and dosing regimen of IV and oral VDRA medications or derivatives (calcitriol, maxacalcitol, falecalcitriol, alfacalcidol, and eldecalcitol) were not permitted. However, dose reduction or discontinuation of VDRA preparations and derivatives were allowed if the serum cCa level was > 11.0 mg/dL after the start of the study treatment. Furthermore, initiation of treatment with VDRA preparations and derivatives or any dose increase was permitted if either of the following conditions were met: corrected serum calcium level decreased below 7.5 mg/dL and remained at � 7.5 mg/dL after the dose increase or initiation of a calcium preparation; or appearance of clinical symptoms potentially attributable to hypocalcemia that did not improve after the initiation or dose increase of a calcium preparation.
The initiation of phosphate binders, calcium preparations, or food with a phosphate binding effect was not allowed for patients who were not already receiving these preparations or food during this period.

Study design and patients
This ad hoc analysis was designed to analyze the efficacy and safety results of the previous phase 3 head-to-head comparison study, stratified by the baseline weekly IV VDRA dose: patients in the evocalcet arm treated with no VDRA as no dose group (NDG); < 1.5 μg/week VDRA as low (L)DG; � 1.5 μg/week VDRA as high (H)DG. The prescribed weekly dose of VDRA derivatives was converted to an equivalent calcitriol dose (e.g. 10 μg of maxacalcitol was equivalent to 1.5 μg of calcitriol). Both male and female patients were included in the present study.

Efficacy and safety endpoints
The efficacy endpoints were 30 weeks of mean serum levels of intact PTH, cCa, phosphorus, and intact and C-terminal FGF23 levels, and their percent changes from baseline, as well as numbers and percentages of patients who achieved the targets of intact PTH (60 to 240 pg/ mL), cCa (8.4 to 10.0 mg/dL), and phosphorus (3.5 to 6.0 mg/dL) during the evaluation period [35,36], stratified by the VDRA dose. Ratios of intact-to-C-terminal FGF23 in all patients by VDRA dose, as well as the mean expression levels of bone turnover markers (bone specific alkaline phosphatase [BAP] and tartrate-resistant acid phosphatase-5b [TRACP-5b]) by VDRA dose were evaluated. The mean daily dose of evocalcet was presented by VDRA dose.
Safety endpoints were incidences of pre-determined hypocalcemia-related (cCa decreased, blood calcium decreased, and hypocalcemia) and upper gastrointestinal tract-related (nausea, vomiting, abdominal discomfort, abdominal distension, and decreased appetite) adverse drug reactions (ADRs) by VDRA dose.

Statistical methods
Efficacy was evaluated in the per protocol set (PPS), which excluded the following patients: those who did not receive treatment with evocalcet, who had no intact PTH measurement after starting the treatment with evocalcet, who did not meet any inclusion criteria or met any of the exclusion criterion, who were prescribed evocalcet for � 28 weeks with an adherence rate of < 70%, who received prohibited concomitant medication or therapy, who did not have two or more intact PTH measurements from three timepoints during the evaluation period (Weeks 28 to 30), or who had a protocol violation that might have affected the efficacy evaluations. Safety was assessed in the safety analysis set, which included all patients except those who did not receive treatment with evocalcet.
For the patient baseline characteristics, categorical data were summarized using frequencies and percentages, and continuous data were summarized using descriptive statistics consisting of the number of patients, mean, and standard deviation by DG. Categorical data were analyzed using the χ 2 test, and continuous data were analyzed using the Kruskal-Wallis test or analysis of variance according to the date distribution. For between-group comparisons of the percentages of patients who achieved the targets, crude differences and 95% confidence intervals were calculated, which were adjusted further for age (< 65 and � 65 years), sex, intact PTH level (< 500 pg/mL and � 500 pg/mL) at baseline and previous cinacalcet treatment. The χ 2 test was used for statistical analysis. Differences in changes in intact PTH, corrected calcium, and phosphorus from baseline to Week 30 among three DGs were analyzed by a repeated linear mixed model. Pearson's correlation coefficient and linear mixed-effects modeling were used to assess the relationship between intact and C-terminal FGF23 levels, and the level of correlation was shown as adjusted R-squared. The ratio of intact-to-C-terminal FGF23 at each time point was normalized to the baseline ratio in each DG. For intact FGF23 levels, those � 80,000 pg/mL were excluded from the analyses. Changes in the ratio of intact-to-Cterminal FGF23 between Week 0 and Week 30 were analyzed by a generalized linear mixed model. All pre-determined ADRs were summarized by preferred term according to the Medical Dictionary for Regulatory Activities version 19.0, and between-group differences were analyzed using the χ 2 test. Statistical analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC, USA), and two-tailed p-values < 0.05 were considered statistically significant.

Patients
Of 320 patients randomized to receive evocalcet in the previous phase 3 head-to-head comparison study [26], 317 patients were included in the safety analysis set and 253 patients were included in the PPS (117, 45, and 91 were treated with no, low, and high IV VDRA, respectively) in this ad hoc analysis.
Patient baseline characteristics were similar among the three DGs in the PPS, including the proportions of males and females (range: males 65.8% to 76.9% and females 23.1% to 34.2%) ( Table 1). However, a significantly higher number of prior cinacalcet users were included in the HDG compared with the other DGs (p < 0.001), and the baseline mean BAP level was lower (p = 0.015) and the C-terminal FGF23 level was higher (p = 0.031) as the concomitant VDRA dose range increased.

Intact PTH, cCa, phosphorus, and bone turnover markers
After the initiation of treatment with evocalcet, the mean intact PTH level gradually decreased in all DGs by Week 30 (NDG vs LDG, p > 0.1; NDG vs HDG, p < 0.0001; LDG vs HDG, p = 0.0025). The mean percent reductions in intact PTH from baseline were also increased throughout the 30 weeks of treatment, irrespective of concomitant VDRA dose ( Fig 1A, S2  Table). The mean cCa level decreased until Week 4 after treatment initiation and remained at a similar level in all DGs with slightly lower levels in the NDG and LDG compared with the HDG (NDG vs LDG, p > 0.1; NDG vs HDG, p = 0.0019; LDG vs HDG, p > 0.1). A similar tendency was observed for the mean percent changes in cCa levels, irrespective of concomitant VDRA dose (Fig 1B, S2 Table). The mean phosphorus levels and mean changes in the phosphorus levels tended to show moderate reductions over the study period (all between-groups, p < 0.0001) (Fig 1C, S2 Table). However, no significant difference was observed for the intact PTH, cCa, or phosphorus level among the three DGs when the levels were adjusted according to their respective baseline levels (all cases, p > 0.95). The mean BAP level was slightly increased at Week 6 and gradually returned to the baseline level at Week 30 in all DGs (Fig 2A). Mean TRACP-5b levels gradually decreased in all DGs throughout the 30 weeks of the study period (Fig 2B).

Intact PTH, cCa, and phosphorus guideline target achievement rates
The proportions of patients who achieved the intact PTH target in the LDG and HDG were slightly higher than that in the NDG, but no significant difference was found among the DGs.

Evocalcet with vitamin D receptor activator
The proportion of patients who achieved the cCa target was significantly higher as the VDRA dose increased (p = 0.043). The proportion of patients who achieved the phosphorus target was similar among the DGs. The proportion of patients who achieved intact PTH, cCa and phosphorus targets was similar among the DGs, although it was slightly higher in the HDG compared with the other DGs (Table 2).

Daily evocalcet doses
The mean daily evocalcet doses were increased at Week 4, when a dose increase was permitted, and showed a gradual increase until the end of the dose adjustment period in all DGs (mean ± standard deviation at Week 27: 3.32 ± 2.38, 3.91 ± 2.46, and 3.34 ± 2.43 mg/day in the

ADRs
Overall, 18.6% (59/317) of patients experienced pre-determined hypocalcemia-related ADRs, and a significant difference was found among the three DGs with the highest incidence rate in the NDG (p = 0.003). The incidence of hypocalcemia in the NDG was the highest compared with the LDG and HDG (p = 0.014). Also, 12.9% (41/317) of patients experienced pre-determined upper gastrointestinal tract-related ADRs without significant differences in the incidence rates (Table 3).

FGF23
The mean intact and C-terminal FGF23 levels in the HDG were higher than those in the NDG and LDG at baseline and throughout the treatment period. After starting treatment with evocalcet, the intact and C-terminal FGF23 levels were decreased in all DGs (Fig 3). The percent reductions from baseline in intact FGF23 and C-terminal FG23 in the LDG were significantly higher than those in the HDG throughout the 30 weeks of treatment (p < 0.005 and p < 0.030, respectively). The ratio of intact-to-C-terminal FGF23 in all DGs was 1.2 from Week 0 to the measurement time point at Week 6, which indicates a higher intact FGF23 level compared with the C-terminal FGF23 level (Fig 4). The ratio in the NDG and LDG decreased to 1.1 at Week 12 and then to 0.9 at Week 30 (vs HDG, p < 0.007); however, the reduction in the HDG was not as marked (1.1 at Week 30). The adjusted R-squared was similar among the DGs in Week 0 and did not show a notable change at Week 30 (Fig 5). The slope of the FGF23 intact and C-terminal relationship at Week

Discussion
The current ad hoc analyses demonstrated that evocalcet was effective at reducing the intact PTH, cCa, phosphorus, TRACP-5b, BAP, and FGF23 levels, irrespective of concomitant IV VDRA. The clinical benefit of evocalcet with IV VDRA was also found for hypocalcemia. Although the difference was not statistically significant, we found that over the 30 weeks of treatment, intact PTH levels tended to be slightly lower in the LDG and HDG compared with the NDG; indeed, > 7% of patients achieved the target with VDRA compared with those receiving evocalcet alone, which indicates that evocalcet and VDRA might have additive effects. Treatment with evocalcet and VDRA showed similar but significant effects on the cCa levels: > 10% patients achieved the target compared with evocalcet alone. Treatment with evocalcet alone decreased cCa levels below the target range in some patients, which was likely prevented by concomitant VDRA, thereby improving the achievement rate. Indeed, patients treated with concomitant VDRA developed hypocalcemia-related ADRs less frequently than those without VDRA. Therefore, evocalcet and VDRA appear to complement each other in the regulation of calcium levels, leading to further clinical improvements. However, unlike intact PTH and cCa, VDRA had no impact on the proportion of patients who achieved the phosphorus target.
Accumulating evidence suggests that elevated FGF23 levels are associated with increased mortality in patients undergoing hemodialysis [7][8][9][10]. Although the mechanism by which elevated circulating FGF23 levels increase mortality is not fully understood, it is accepted that FGF23 levels should be better controlled [15]. As previously reported for cinacalcet [12], our results showed that evocalcet decreased intact and C-terminal FGF23 levels. However, overall serum FGF23 levels tended to be higher as the VDRA dose increased, consistent with previous studies [30][31][32]. Furthermore, while the percent changes in the HDG stopped decreasing after Week 12, those in the LDG kept decreasing, which suggests that a combination of low range IV VDRA and evocalcet provides better control over FGF23 levels.
A lowered intact-to-C-terminal FGF23 ratio indicates a reduction in FGF23 synthesis; therefore, our results suggest that evocalcet decreased FGF23 levels by suppressing FGF23 synthesis irrespective of concomitant VDRA, although this effect was significantly lower in the HDG compared with the other DGs partly because VDRA stimulates FGF23 synthesis. The suppression of FGF23 synthesis by evocalcet was further supported by our finding that the slope at Week 0 was increased at Week 30 with the highest slope change found in the NDG. In addition to FGF23, favorable effects of the combination therapy were found for levels of the bone turnover markers TRACP-5b and BAP. The timing of the changes in the FGF23 coincided with that of BAP. Because FGF23 is synthesized in osteoblasts and osteocytes [5,6], it would be of clinical interest to elucidate any interactions among these markers and their clinical implications on the prognosis of SHPT in responding to a combination therapy with calcimimetics and VDRA. Furthermore, because elevated levels of FGF23 and bone turnover markers have been presented as prognostic factors [7,12,37,38], further studies are needed to evaluate the long-term effects of this combination therapy.
We observed the clinical benefit of combination therapy with evocalcet and VDRA for predetermined hypocalcemia-related ADRs. Although upper gastrointestinal tract-related ADRs were slightly increased by the addition of VDRA, this increase was negligible, and no notable new hypocalcemia-or upper gastrointestinal tract-related safety concerns were observed.
In this study, the daily evocalcet dose in the LDG was slightly higher than that in the other DGs. Because evocalcet and VDRA both reduce serum intact PTH levels, patients receiving the lower VDRA dose range were assumed to be treated with a higher range of evocalcet daily doses to supplement the efficacy of VDRA. The combination of IV VDRA and evocalcet dose ranges applied to patients in the LDG appeared to be more beneficial than in the HDG because LDG patients had equivalent efficacy to the HDG but with potentially better long-term prognosis related to lower phosphorus and FGF23 levels. However, differences among the three DGs obtained in this study, such as an elevated FGF23 level [29][30][31][32][33][34], and/or differential patient baseline characteristics that included a higher proportion of patients with prior cinacalcet use in the HDG, might have been a consequence of the ongoing VDRA treatment. A post hoc analysis of the previously conducted Evaluation of Cinacalcet Therapy to Lower Cardiovascular Events (EVOLVE) trial, in which the effects of cinacalcet on cardiovascular disease were investigated in severe SHPT patients on maintenance hemodialysis treatment, reported that, in most patients, the doses of cinacalcet, VDRA, and phosphate binders were not adjusted just after or at � 14 days after the onset of hypocalcemia [39], which indicates that further studies are needed to confirm whether a high dose range of VDRA is beneficial for the treatment of SHPT patients with oral calcimimetics. Considering the advantages and disadvantages of the combination therapy, treatment options and doses need to be finely adjusted dependent on individual patient disease state, conditions, and characteristics.
This study had some limitations. First, differences in the 30 weeks of mean changes and percent changes from baseline in the intact and C-terminal FGF23, BAP, and TRACP-5b levels were not statistically tested within and among the three DGs. Therefore, any longitudinal mean changes and between group differences in levels need to be interpreted as tendencies. In addition, all patients were Japanese, the study had a small sample size, and patients were treated with evocalcet only up to 30 weeks. Although evocalcet was developed in Japan and has only recently been approved for the treatment of SHPT in patients on maintenance dialysis, it is expected that long-term studies will be conducted in the near future to determine the efficacy and safety of evocalcet in other global populations with larger sample sizes.
In conclusion, treatment with evocalcet improved the achievement rate of the serum cCa target, decreased FGF23 levels by suppressing FGF23 synthesis, and decreased the incidence of hypocalcemia in the presence of VDRA, demonstrating the additive benefits of the combination therapy in SHPT patients.